Patient-specific, mechanical self-locking, femoral and tibial surgical cutting jigs

ABSTRACT

Jigs for guiding femur and tibia resectioning in knee surgery contain bone-jig contact surfaces and a cutting guide as a single unitary piece. Contact surfaces are curvilinear surfaces formed into ends of projections from a jig base. Each jig has three pairs of contact surfaces selected to abut low-wear, lateral and medial, articular surface features, such that only one self-locking position against the bone (or cartilage) is possible and the integral cutting guide will define only one cut plane for the resectioning. An improved rotational transformation that converts scan views into desired proper axes is based on projections of rotated coordinates onto the plane of rotation to produce parameters that closely correspond to the joint surfaces in the desired jig coordinates.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. provisional application No.62/628,117, filed Feb. 8, 2018.

TECHNICAL FIELD

The invention relates to jigs for guiding bone resectioning in kneereplacement surgery, and to the manufacture of such jigs, such that eachjig is patient-specific with custom specifications determined from MRIslices of a patient's tibio-femoral joint region.

BACKGROUND ART

Femoral and tibial surgical cutting jigs are used to guide boneresectioning in knee replacement surgery. Each jig contains both thevarious bone-jig contact surfaces and a cutting guide defining a cutplane. In order that the cut planes are correct when the respective jigsare installed during surgery, each jig must be custom manufactured tocorrespond to a patient's own femur and tibia. Magnetic resonanceimaging (MRI) of a patient's tibio-femoral joint region is performedprior to surgery to define the parameters needed to manufacturepatient-specific jigs.

One problem in parameterizing the surface features from the MRI scans isthat the coronal, axial and sagittal view orientations of actual scansdo not necessarily (and usually do not) coincide with desired orthogonalaxes for creating the jig, necessitating one or more rotationaltransformations of the respective scan slices with simultaneous rotationof all these views (coronal, axial and sagittal). Unfortunately, a“simple” Euler transformation is insufficient to obtain the propersimultaneous rotations of the image slices because it incorrectlyassumes that the planes for the coronal, axial and sagittal slices beingrotated are themselves orthogonal to each other. Consequently,performing a rotation θ of a coronal slice in an x-z plane alters theaxial and sagittal view coordinates as well; and likewise, for arotation φ of an axial slice in an x-y plane, and rotation ψ of asagittal slice in a y-z plane. With an Euler transformation, as many as15 individual iterations of the transformation may be required beforethe slices in the different view planes converge to fixed values, andeven then, may still be wrong.

SUMMARY DISCLOSURE

Patient-specific, femoral and tibial surgical cutting jigs for boneresection are provided that are mechanical self-locking with respect tofeatures in the tibio-femoral joint region. Each jig is a single unitarypiece combining a set of bone-jig contact surfaces and bone cuttingguide defining a cut plane. The set of contact surfaces are curvilinearsurfaces formed onto ends of planar fins projecting from a jigsubstrate. The curvilinear surfaces are positioned to abut respectivelateral and medial articular surface features in the tibio-femoral jointregion such that the unitary piece has one and only one mechanicalself-locking position.

Bone-jig contact specifications (including any cartilage on the bone asalso a part of the bone surface) are computed from a series of coronal,axial and sagittal image slices obtained by magnetic resonance imaging(MRI) of a patient's tibio-femoral joint region. MRI image slices thatshow specified lateral and medial articular surface features in thetibio-femoral joint region are selected. Rotational transformations ofthe selected coronal, axial and sagittal MRI image slices ontoorthogonal jig coordinates are iteratively performed, wherein eachiteration of a transformation in some specified plane of rotation isaccompanied by a projection of rotated coordinates onto that plane ofrotation. From these transformed image slices, patient-specificparameters are characterized for specified lateral and medial articularsurface features in the tibio-femoral joint region to thereby specify aset of bone-jig contact surfaces and a cut plane. Thus, the curvilinearsurfaces of each jig are characterized by custom patient-specificparameters derived from measurements from selected coronal, axial andsagittal MRI slices of the tibio-femoral joint that have been subject toiterated rotational transformations onto orthogonal jig coordinates.

Accordingly, femoral and tibial surgical jigs are manufactured havingcurvilinear surfaces positioned according to the transformed imageslices. Each jig is in the form of a single unitary piece combining abone cutting guide and a set of curvilinear surfaces formed onto ends ofprojections from a jig substrate. The curvilinear surfaces abutrespective lateral and medial articular surface features in thetibio-femoral joint region of the patient such that the jig has one andonly one mechanical self-locking position and the bone cutting guidedefines the specified cut plane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1F are respective front, back, right, left, top andbottom plan views of a femur jig in accord with the present invention.

FIGS. 1G and 1H are first and second perspective views of the femur jigof FIGS. 1A through 1F.

FIGS. 2A through 2F are respective front, back, right, left, top andbottom plan views of a tibia jig in accord with the present invention.

FIGS. 2G and 2H are first and second perspective views of the tibia jigof FIGS. 2A through 2F.

FIG. 3 is a sagittal section of a right knee joint.

FIG. 4 is a plan view of a lower extremity of a right femur.

FIG. 5 is a plan view of an upper extremity of a right tibia.

FIGS. 6A through 6C are respective coronal, axial and sagittal MRI scanimages of a knee joint.

FIG. 7 is a perspective a femur illustrating scan and translatedcoordinate axes.

FIGS. 8A through 8C are respective coronal, axial and sagittaltranslated scan images showing coordinate planes and rotation anglesoverlaid upon the images.

FIGS. 9A through 9C are views of original and transformed coordinateaxes for respective coronal, axial and sagittal rotationaltransformations.

FIGS. 10A through 10D are perspective views of femoral jig and femurthat illustrate steps in aligning the femur jig and securing the jig tothe femur with pins.

FIGS. 11A through 11C are perspective views of tibial jig and tibia thatillustrate steps in aligning the tibial jig and securing the jig to thetibia with pins.

DETAILED DESCRIPTION

The invention relates to jigs for guiding bone resectioning in kneereplacement surgery. Each jig, one for the femur and another for thetibia, contains both the various bone-jig contact surfaces and thecutting guide as a single unitary piece. For purposes of defining jigparameters, note we shall consider and treat any cartilage on therelevant bone as also constituting a part of the bone surface that thejig will contact. Hence, any reference to bone-jig contact surfaces willalso include any cartilage-jig contact surfaces. The contact surfacesare curvilinear surfaces formed into ends of planar fins that projectfrom the jig base or substrate. Each jig has three (3) pairs of contactsurfaces selected to abut low-wear, lateral and medial, articularsurface features, such that the jig has one and only one possibleself-locking position against the bone and so the jig's integral cuttingguide will define one and only one cut plane for the bone resectioning.

With reference to FIGS. 1A through 1H, a jig for guiding theresectioning of a femur is seen. The femoral jig has a front plate orblock 11 that will abut against an anterior surface of the end of afemur, and an end plate or block 12 that will abut against the jointsurface of the femur. The cutting guide may be in the form of two planarslots 18 and 19 extending from lateral and medial sides in the frontplate or block 11. The front plate or block 11, end plate or block 12,and cutting guide 18 and 19 together form a single-piece unitary jigbody of solid material that will fit against the femur in one and onlyone way, thereby establishing the cutting plane for the resectioning.

To ensure this single possible fitting of the jig to the femur, therespective plates or blocks 11 and 12 of the jig have sets ofprojections with curved contact surfaces 13′ through 17′ which aredimensioned according to a specific patient's bone dimensions. For thefemur, medial and lateral anterior feet 13 and 14 of the femoral jigcontact (a) anterior sides of the lateral and medial condyles, whilemedial and lateral posterior feet 15 and 16 of the jig contact (b) thedistal condylar surfaces. A short posterior projection 17 from the jointof the front and end plates 11 and 12 of the jig also contacts (c) thetrochlear groove surfaces. The medial and lateral anterior feet 13 and14 extend rearward from the front plate or block 11, one on the medialside 13 and one on the lateral side 14 and have concave interiorsurfaces 13′ and 14′ whose placement and separation from one anotherclosely match the placement and separation of the anterior sides of therespective lateral and medial condyles. Medial and lateral posteriorfeet 15 and 16 extend in the inferior direction from posterior ends ofthe end plate or block 12, again one on the medial side 15 and one onthe lateral side 16 and have concave inferior surfaces 15′ and 16′ whoseplacement and separation closely match those of the respective convex,lateral and medial, distal condylar surfaces of the femur. A shortposterior projection 17 extending above the end plate or block 12 at ornear is junction with the front plate or block 11 has a convex curvedsurface 17′ that contacts trochlear groove surfaces between the medialand lateral condyles of the femur. Holes 20A-20E for pins allow the jigto be secured to the femur. A notch or groove 21 in the anterior plate11 aids in jig alignment verification.

With reference to FIGS. 2A through 2H, a jig for guiding theresectioning of a tibia is seen. The tibial jig has a main medial plateor block 23 that will abut against anterior and medial surfaces of theend of a tibia, and an end extension 25 of a front plate or block 24that will abut against the joint surface of the tibia. The cutting guidemay be in the form of two planar slots 32 and 33 extending from anteriorand posterior sides of the medial plate or block 23. The medial mainplate or block 23, the front plate or block 24 with its end extension25, and the cutting guide 32 and 33 together form a single-piece unitaryjig body of solid material that will fit against the tibia in one andonly one way, thereby establishing the cutting plane for theresectioning. Holes 34A-34E for pins allow the jig to be secured to thetibia.

To ensure this single possible fitting of the jig to the tibia, therespective plates or blocks of the jigs have sets of projections withcurved contact surfaces which are dimensioned according to a specificpatient's bone dimensions. For the tibia, the main block 23 of thetibial jig contacts (a) the medial and/or anterior surface of thetibia's shaft along curved surfaces 26′ and 27′, while posterior feet 25have two sets of projections 28-31 that contact (b) the superiorarticular surfaces of the lateral and medial condyles at positionsanterior of the spine and (c) articular surfaces on lateral and medialslopes of the tibial spine itself. The presence of osteophytes generallydoes not adversely impact the proper fit of the jigs. Specifically, themain medial plate or block 23 has a concave extension 26 on its interior(boneward) side that contacts the medial surface of the tibia's shaft.Additionally, the front plate or block 24 may have a concave extension27 on its lateral end that continues the curve defined by the medialblock's extension and which contacts the anterior surface of the tibia'sshaft. The end extension 25 projects from a superior (upper) surface ofthe front plate or block 24 and has a pair of posterior feet (i.e.medial and lateral feet) with respective sets of downward projections28-31. One set of projections (one on each posterior foot), i.e. themore anteriorly located set 28 and 29, has concave curvatures 28′ and29′ that contact superior articular surfaces of respective medial andlateral condyles at positions anterior of the tibial spine. The secondset of projections 30 and 31 (again, one on each posterior foot)likewise has concave curvatures 30 and 31 that contact articularsurfaces on respective medial and lateral slopes of the tibial spineitself.

FIGS. 3, 4 and 5 illustrate the features near the knee joint with whichthe jigs make contact. In FIG. 3, the lower portion of the femur 37 andthe upper portion of the tibia are seen to meet at respective jointsurfaces 41 and 42. The location of the patella 39 and correspondingconnecting ligaments is also visible. In FIG. 4, the lower extremity 41of the femur is seen to include a lateral condyle 43 and medial condyle44 with an intercondylar region forming a trochlear groove 45. Theanterior surface of the femur is at the region 46. In FIG. 5, the upperextremity 42 of the tibia is likewise seen to have both a medial condyle47 and a lateral condyle 48. The anterior surface of the tibia is at theregion 49.

One aspect of the invention is that each jig is patient-specific withcustom dimensions determined from MRI slices of the patient'stibio-femoral joint region. Three series of MRI slices are taken of theknee to create respective coronal (front), axial (top) and sagittal(side) views, respectively seen in FIGS. 6A, 6B and 6C. Each “slice” isactually 2 to 3 mm thick and there is about a 1 mm gap betweensuccessive slices of the same view angle. Besides slices of the knee, itmay be advantageous to obtain at least coronal MRI scans of thefemur/hip and tibia/ankle areas as well to fully characterize the lowerlimb alignment. But in comparison to computationally-intensive fullsegmentation approaches, only a select small number of slices of theknee joint area (5 or 6 for each bone) are needed to identify andparameterize the articular surface features for constructing the jigs.These are slices associated with low wear portions of the lateral andmedial condyle surfaces and the intercondylar regions (with thetrochlear groove and tibial spine), seen especially well in the coronalview (FIG. 6A). Axial and sagittal views (FIGS. 6B and 6C) can defineanterior surfaces of the bones immediately adjacent to the joint.

With reference to FIG. 7, one problem in parameterizing the surfacefeatures from the MRI scans is that the coronal, axial and sagittal vieworientations of actual scans do not necessarily (and usually do not)coincide with desired orthogonal axes (x, y, z) for creating the jig,necessitating one or more rotational transformations (θ, φ, ψ) of therespective scan slices. Unfortunately, a “simple” Euler transformationis insufficient to obtain the proper rotations of the image slicesbecause it incorrectly and simultaneously assumes that the planes forthe actual coronal (x-z), axial (x-y) and sagittal (y-z) image slicesbeing rotated are themselves orthogonal to each other. Consequently,performing a rotation θ of a coronal slice in an x-z plane alters theaxial and sagittal view coordinates as well; and likewise, for arotation φ of an axial slice in an x-y plane, and rotation ψ of asagittal slice in a y-z plane. With an Euler transformation, as many as15 iterations of the transformation may be required before the slices inthe different view planes converge to fixed values, and even then, maystill be wrong.

With reference to FIGS. 9A, 9B and 9C, an improved rotationaltransformation method for converting the scan views into the desiredproper axes reduces the number of iterations to three and producesparameters that correspond much more closely to the joint surfaces inthe desired jig coordinates. The improved transformation matrix is basednot only on planar rotations (as in Euler), but also on a projection ofthe rotated coordinates onto the plane of rotation (e.g., projection ofx′, y′, z′ coordinates—obtained from x-y plane rotation θ to an x′-y′plane—onto x′, y′, 0 coordinates) before proceeding to the nextrotation.

We begin with a translation of the scan origin (x₀, y₀, z₀) to aspecified center (x_(c), y_(c), z_(c)) of the joint anatomy, such as theintercondylar space where the anterior cruciate ligament attaches to thetibia.

$\begin{bmatrix}x \\y \\z\end{bmatrix} = {{{\begin{bmatrix}A_{11} & A_{12} & A_{13} \\A_{21} & A_{22} & A_{23} \\A_{31} & A_{32} & A_{33}\end{bmatrix}\mspace{14mu}\left\lceil \begin{matrix}x_{c} \\y_{c} \\z_{c}\end{matrix} \right\rceil} + {\left\lceil \begin{matrix}{\Delta\; x} \\{\Delta\; y} \\{\Delta\; z}\end{matrix} \right\rceil\mspace{14mu}{{where}\mspace{14mu}\begin{bmatrix}{\Delta\; x} \\{\Delta\; y} \\{\Delta\; z}\end{bmatrix}}}} = {\begin{bmatrix}{- x_{0}} \\{- y_{0}} \\{- z_{0}}\end{bmatrix}.}}$

Next, we rotate the coordinates with respect to the newly centeredorigin. The rotations can be performed in any order, but we start with acoronal rotation θ about the x-z plane, followed by an axial rotation φabout a transformed x′-y′ plane, then sagittal rotation ψ about afurther transformed y″-z″ plane.

The first rotation is represented in FIG. 9A. The coronal rotation θabout the x-z plane transforms the x-axis to an x′-axis extending from(0, 0, 0) to (x₁, 0, z₁), where θ=tan⁻¹(z₁/x₁).

$\Theta = \begin{bmatrix}{\cos\;\theta} & 0 & {{- \sin}\;\theta} \\0 & 1 & 1 \\{\sin\;\theta} & 0 & {\cos\;\theta}\end{bmatrix}$An x-y plane point transformation to x′, y′, z′ coordinates follows:

$\begin{bmatrix}x_{2}^{\prime} \\y_{2}^{\prime} \\z_{2}^{\prime}\end{bmatrix} = {{\left\lceil \begin{matrix}{\cos\;\theta} & 0 & {{- \sin}\;\theta} \\0 & 1 & 1 \\{\sin\;\theta} & 0 & {\cos\;\theta}\end{matrix} \right\rceil\mspace{14mu}\begin{bmatrix}x_{2} \\y_{2} \\0\end{bmatrix}} = \begin{bmatrix}{\cos\;{\theta \cdot x_{2}}} \\y_{2} \\{\sin\;{\theta \cdot x_{2}}}\end{bmatrix}}$A y-z plane point transformation to x′, y′, z′ coordinates follows:

$\begin{bmatrix}x_{3}^{\prime} \\y_{3}^{\prime} \\z_{3}^{\prime}\end{bmatrix} = {{\begin{bmatrix}{\cos\mspace{11mu}\theta} & 0 & {{- \sin}\;\theta} \\0 & 1 & 1 \\{\sin\;\theta} & 0 & {\cos\;\theta}\end{bmatrix}\mspace{14mu}\begin{bmatrix}0 \\y_{3} \\z_{3}\end{bmatrix}} = \begin{bmatrix}{{- \sin}\;{\theta \cdot z_{3}}} \\y_{2} \\{\cos\;{\theta \cdot z_{3}}}\end{bmatrix}}$

The second rotation is represented by FIG. 9B. The axial rotation φtransforms the x′-axis to an x″-axis extending from (0,0,0) to(x′₂,y′₂,0), where φ=tan⁻¹(y′₂/x′₂)=tan⁻¹ (y₂/cos θ·x₂).

$\Phi = \begin{bmatrix}{\cos\;\varphi} & {{- \sin}\;\varphi} & 0 \\{\sin\;\varphi} & {\cos\;\varphi} & 0 \\0 & 0 & 1\end{bmatrix}$An y′-z′ plane point transformation to x″, y″, z″ coordinates follows:

$\begin{bmatrix}x_{3}^{\prime\prime} \\y_{3}^{\prime\prime} \\z_{3}^{\prime\prime}\end{bmatrix} = {{\begin{bmatrix}{\cos\;\varphi} & {{- \sin}\;\varphi} & 0 \\{\sin\;\varphi} & {\cos\;\varphi} & 0 \\0 & 0 & 1\end{bmatrix}\;\begin{bmatrix}x_{3}^{\prime} \\y_{3}^{\prime} \\z_{3}^{\prime}\end{bmatrix}} = {\begin{bmatrix}{{{- \sin}\;{\theta \cdot \cos}\;{\varphi \cdot z_{3}}} - {\sin\;{\varphi \cdot y_{3}}}} \\{{{- \sin}\;{\varphi \cdot \sin}\;{\theta \cdot z_{3}}} + {\cos\;{\varphi \cdot y_{3}}}} \\{\cos\;{\theta \cdot z_{3}}}\end{bmatrix}.}}$

The third rotation is represented by FIG. 9C. The sagittal rotation ψtransforms the z″-axis to an z′″-axis extending from (0, 0, 0) to (0,y″₃, z″₃), where ψ=tan⁻¹(y″₃/z″₃)=tan−1 [(−sin φ·sin θ·z₃+cos φ·y₃)/cosθ·z₃].

$\Psi = \begin{bmatrix}1 & 0 & 0 \\0 & {\cos\;\psi} & {{- \sin}\;\psi} \\0 & {\sin\;\psi} & {\cos\;\psi}\end{bmatrix}$Yet another plane point transformation to x′″, y′″, z′″ coordinatesfollows:

$\begin{bmatrix}x^{\prime\prime\prime} \\y^{\prime\prime\prime} \\z^{\prime\prime\prime}\end{bmatrix} = {{\begin{bmatrix}1 & 0 & 0 \\0 & {\cos\;\psi} & {{- \sin}\;\psi} \\0 & {\sin\;\psi} & {\cos\;\psi}\end{bmatrix}\;\begin{bmatrix}x^{\prime\prime} \\y^{\prime\prime} \\z^{\prime\prime}\end{bmatrix}} = {\begin{bmatrix}A_{11} & A_{12} & A_{13} \\A_{21} & A_{22} & A_{23} \\A_{31} & A_{32} & A_{33}\end{bmatrix}\mspace{14mu}\left\lfloor \begin{matrix}x \\y \\z\end{matrix} \right\rfloor}}$where:

A₁₁=cos φ·cos θ

A₁₂=−sin φ

A₁₃=−cos φ·sin θ

A₂₁=cos ψ·sin φ·cos θ−sin ψ·sin θ

A₂₂=−cos ψ·sin φ−sin ψ·cos φ

A₂₃=−cos ψ·sin φ·sin θ−sin ψ·cos θ

A₃₁=sin ψ·sin φ·cos θ+cos ψ·sin θ

A₃₂=sin ψ·cos φ

A₃₃=−sin ψ·sin φ·sin θ+cos ψ·cos θ

This process successive rotations and projections is then iterated anumber of times until changes in transformed images reduce belowspecified thresholds ε.

$\begin{bmatrix}x^{\prime\prime\prime} \\y^{\prime\prime\prime} \\z^{\prime\prime\prime}\end{bmatrix}_{i + 1} = {\begin{bmatrix}A_{11} & A_{12} & A_{13} \\A_{21} & A_{22} & A_{23} \\A_{31} & A_{32} & A_{33}\end{bmatrix}_{i}\mspace{11mu}\begin{bmatrix}x \\y \\z\end{bmatrix}}_{i}$where i=1, 2, 3, . . . .

${T_{i} = \begin{bmatrix}A_{11} & A_{12} & A_{13} \\A_{21} & A_{22} & A_{23} \\A_{31} & A_{32} & A_{33}\end{bmatrix}_{i}}\;$ ${F = {\prod\limits_{i}^{n}\; T_{n - i + 1}}},$where F is total transformation matrix, n is total number oftransformations and T_(n-i+1) is (n−i+1^(st)) transformation matrix.Combining the separate transformations into a total transformationmatrix is possible here even where the original coronal, axial andsagittal image views are not actually orthogonal to one another. Theiteration criteria (which can be different for the coronal, axial andsagittal views; for example, more stringent for the coronal view andleast stringent for the sagittal view) are:|θ_(i+1)−θ_(i)|<ε_(c)|φ_(i+1)−φ_(i)|<ε_(a)|ψ_(i+1)−ψ_(i)|<ε_(s)Once the image has been properly transformed, the various dimensions ofjoint features for the femur and tibia can readily be calculated andused to construct the femoral and tibial jigs of FIGS. 1 and 2.

With reference to FIGS. 10A through 10D, the femoral jig or guide isinstalled onto the femur during surgery according to a carefullyprescribed procedure. The jig, if constructed according to thetransformed MRI scan images will fit one and only one way onto the endof the femur as defined by the curved contact surfaces of the jig. Withthe knee moderately flexed, the medial synovium is released from themid-point of the patella proximally to a point superior to the trochleargroove. The posterior patellar tendon fat pad is excised from the jointline to the tibial tubercle. With the knee flexed to approximately 70°,retract the quadriceps muscle in the usual fashion to expose theanterior femoral cortex. Displace the patella laterally as usual toobtain full exposure. Removal of osteophytes is at the surgeon's optionand their presence is generally not a detriment to proper fit of theguides (due to the choice of contact points of the jig contact surfacesto low-wear regions on the femur). Likewise, removal of osteophytes doesnot adversely impact guide fit. Place the femoral jig or guide onto theend of the femur. Initial placement is accomplished by orienting theguide and the condyle contact feet 15 and 16 slightly above themid-point of the condylar curve as to allow the superior feet to makeinitial contact with the epicondylar area. While maintaining lightpressure on the guide, rotate it posteriorly until anterior feet 13 and14 and posterior feet 15 and 16 of the guide make light contact with theanterior lateral and medial sides of the condyles and the distalcondylar surfaces, as shown in FIG. 10A. From the medial and lateralsides, the curved contacts 13, 14, 15 and 16 should light touch thesurface of the tissue without using excess force or direct pressure. Asmall (less than 1 mm) gap may sometimes occur somewhere along thecontact curves. An additional contact 17 in the trochlear groove willnot be visible. A visual indicator in the form of a V-shaped notch orslot 21 verifies that the guide is correctly aligned with respect to thelong axis of the femur. When properly placed, a pin 51 placed in thisnotch 21 will point toward the center of the femoral head, as seen inFIG. 10C. Additionally, it will be seen to be located directly over themidpoint of the condylar notch. Once all of the positioning points arecorrectly verified the projected cut plane defined by the planar cuttingguide slots 18 and 19 in the jig should be assessed before proceeding,for example by employing a resection checker or “angel-wing” passedthrough the cut slot. The depth of both the medial and lateral cutsshould verified as they affect the varus/valgus angle. Additionally,resectioning along the defined cut plane should not lead to notching orgapping of the implant following use of a 4:1 (chamfer) cutting block.As seen in FIG. 10B, the final anterior cut plane should just skim theanterior surface of the femur. After verification of the cuts, distalpins are placed through holes 20A and 20B while holding the jig inplace. Using care that the guide is not skewed or flexed, anterior pinsare placed through holes 20C and 20D while still holding the jig inplace. After removal of the lateral distal pin, it is relocated to adiagonal stabilization pin location through hole 20E to reduce thepossible guide shifting due to saw vibration. The medial distal pin isleft in place until the lateral condyle cut is complete. After thelateral femur condyle pin is removed, the lateral condyle itself isremoved using an orthopedic saw, as seen in FIG. 10D. A saw blade of atleast 110 mm length will likely be needed to fully reach through thecondyle in some cases. A blade thickness of 1.27 mm is recommended.

With reference to FIGS. 11A-11C, next, the tibial jig or guide isinstalled onto the tibia during surgery according to a carefullyprescribed procedure. The jig, if constructed according to thetransformed MRI scan images will fit one and only one way onto the endof the tibia as defined by the curved contact surfaces of the jig. Thejig is placed against the medial and anterior side surfaces of the tibiaand the top of the tibial plateau with the medial plate or block 23against the medial side surface of the tibia, the anterior plate orblock 24 against the anterior side surface of the tibia, and theposterior foot extension 25 with wing projections 28-31 above the tibialplateau. For the medial and anterior sides of the tibia, the curvedcontacts 26 and 27 abut the tibia as seen from above in FIG. 11A. Forthe tibial plateau, the curved underside of the medial projections 28and 30 contact the medial condyles of the tibia at respective anteriorand posterior positions, as seen if FIG. 11B. Likewise, the curvedunderside of the lateral projections 29 and 31 will contact the lateralcondyles of the tibia at respective anterior and posterior positions.While holding the jig in place, proximal pins are inserted through holes34C and 34D, then anterior pins are inserted through holes 34A and 34B.The proximal pins may then be removed, and the jig stabilized byinstalling one of them through the diagonal hole 34E at the posteriorend of the medial plate 23. After re-verifying the cut angle(medial/lateral and posterior slopes) is correct, the tibia may be cutas seen in FIG. 11C by inserting the saw into cut plane slots 32 and 33.Once the end of the tibia has been completely cut, the pins and tibialjig are removed, and the remainder of the total knee replacement surgerycan continue.

What is claimed is:
 1. A surgical jig for bone resection in atibio-femoral joint region, comprising: a single unitary piece combininga set of bone jig contact surfaces and a bone cutting guide defining acut plane, the set of contact surfaces being curvilinear surfaces formedonto ends of projections from a jig substrate, the curvilinear surfacespositioned to abut respective lateral and medial articular surfacefeatures in the tibio-femoral joint region such that the unitary piecehas one and only one mechanical self-locking position, the curvilinearsurfaces further characterized by custom patient-specific parametersderived from measurements from selected coronal, axial and sagittalmagnetic resonance imaging (MRI) image slices of the tibio-femoraljoint, the image slices having been subject to a set of rotationaltransformations onto orthogonal jig coordinates including at least onecoronal rotation, at least one axial rotation, and at least one sagittalrotation, wherein each transformation in some specified plane ofrotation is accompanied by a projection of rotated coordinates onto thatplane of rotation, each coronal rotation in an x-z plane by an angle θis followed by x-y and y-z plane point transformations, each axialrotation in a x-y plane by an angle φ is followed by y-z and x-z planepoint transformations, and each sagittal rotation in a y-z plane by anangle Ψ is followed by x-z and x-y plane point transformation, where anx coordinate axis coincides with a lateral-medial direction, a ycoordinate axis coincides with an anterior-posterior direction, and a zcoordinate axis coincides with a bone long axis, each rotationaltransformation after a first transformation being a rotation followed bypoint transformations in a set of transformed planes resulting from theprevious rotational transformation.
 2. The surgical jig as in claim 1,wherein the jig is a femoral jig having a front plate coupled to an endplate at an elbow joint, the front plate having at least one planar slottherein coinciding with a desired cut plane when the jig is installedonto a femur, the front plate having a pair of anterior feet withcurvilinear surfaces thereon for contact with anterior sides ofrespective medial and lateral condyles of the femur, the end platehaving a pair of posterior feet with curvilinear surfaces thereon forcontact with condylar surfaces of the respective medial and lateralcondyles, the end plate also having a posterior projection proximate tothe elbow joint and having a convex curvilinear surface for contact withtrochlear groove surfaces in an intercondylar region of the femur. 3.The surgical jig as in claim 1, wherein the jig is a tibial jig having amain medial block and a front plate coupled to the main medial block atan elbow joint, the main medial block having at least one planar slottherein coinciding with a desired cut plane when the jig is installedonto a tibia, an end extension projecting from a superior posteriorsurface of the front plate, the end extension having pairs of medial andlateral posterior feet with downward projections, the main medial blockhaving a concave extension on an interior side of the elbow joint forcontact with a side surface of the tibia, the downward projections ofthe posterior feet having underside curvilinear surfaces for contactwith the medial and lateral condyles of the tibia at a position anteriorto the tibial spine.
 4. The surgical jig as in claim 1, wherein the setof rotational transformations with plane point transformations isrepeated until changes in transformed images reduce below one or morespecified thresholds.